1. Field of the Invention
The present invention relates to a power steering apparatus.
2. Description of the Related Art
Conventionally, in a power steering apparatus, a structure is made to have a control valve for switching and connecting a pump side supply flow passage and a tank side return flow passage to a first chamber and a second chamber of a power cylinder in accordance with a steering operation. It interposes a damper valve between each of the first chamber and the second chamber of the power cylinder and the control valve. Further, the damper valve is structured, as described in Japanese Utility Model Application Laid-Open Publication No. 64-35180, to have a housing, a partition member for partitioning an inner portion of the housing into a power cylinder side and a control valve side. It also has a first valve apparatus provided in the partition member and allows only a supply direction flow from the control valve side to the power cylinder side, and a second valve apparatus provided in the partition member and applys a damping force to a return direction flow from the power cylinder side to the control valve side.
In this power steering apparatus, when steering to the right or the left, fluid pressurized and fed by a pump is fed from the control valve to any one oil chamber of the first chamber and the second chamber in the power cylinder, and a propelling force is applied to a rack shaft passing through the power cylinder, thereby assisting the right or left steering force. At the same time, the fluid in another oil chamber in the power cylinder is returned to a tank via the control valve. On the other hand, when the steering force is neutral, the fluid pressurized and fed by the pump is returned to the tank from the control valve, whereby the fluid is not supplied and discharged to the first chamber and the second chamber of the power cylinder.
Further, in the power steering apparatus, since the respective damper valves are connected to the first chamber and the second chamber of the power cylinder, a neutral stability of the power cylinder in neutral steering operation is improved and a high speed straight drive performance of the vehicle is improved. That is, in neutral steering, since the fluid is not supplied from the control valve side to the power cylinder side, the first valve apparatuses of the respective damper cylinders are in a closed state, and the closed state of the second valve apparatus is maintained as far as a road reaction force applied to the power cylinder is not over the damping force of the second valve apparatuses in the respective damper valves, whereby the fluid discharge from the first chamber or the second chamber of the power cylinder is not generated, and the power cylinder maintains an immobility, that is, the neutral stability is improved.
However, since the conventional damper valve is structured, as described in Japanese Utility Model Application Laid-Open Publication No. 64-35180, such that the partition member is screwed onto the housing, there are disadvantages such that it is necessary to apply a screw formation process to the partition member. A tool exclusive for screwing the partition member is required, whereby a screwing operability is not good due to a small-sized part, a countermeasure for preventing a slackness generated due to a vibration is required, and the like.
In this case, in a structure of fixing the partition member by a circlip, in addition that the circlip is required, a re-detachability at maintenance is poor. Further, in the case of pressing and fixing the partition member, a re-detachability at maintenance is significantly poor.
An object of the present invention is to intend a stability of a damper characteristic by easily and securely fixing a partition member constituting a damper valve to a housing in a power steering apparatus, and improve a dissembling and assembling performance at maintenance.
According to the present invention, there is disclosed a power steering apparatus which has a control valve for switching and connecting a pump side supply flow passage and a tank side return flow passage to a first chamber and a second chamber of a power cylinder in accordance with a steering operation and interposing a damper valve between each of the first chamber and the second chamber of the power cylinder and the control valve, wherein a damper valve has a housing, a partition member for partitioning an inner portion of the housing into a power cylinder side and a control valve side, a first valve apparatus provided in the partition member and allowing only a supply direction flow from the control valve side to the power cylinder side, and a second valve apparatus provided in the partition member and applying a damping force to a return direction flow from the power cylinder side to the control valve side, and wherein the damper valve has a cap attached to the housing and holds the partition member between the cap and the housing.